﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Common
{
   public class ShortUrlGenerator
    {
        /// <summary>
        /// 获取短链接第几个(共四个6位字符串)
        /// </summary>
        /// <param name="iIndex"></param>
        /// <param name="sLongUrl"></param>
        /// <returns></returns>
        public static string SetShortUrl(int iIndex, string sLongUrl)
        {
            string strShort = "";
            try
            {
                String[] aResult = ShortUrlGenerator.GetshortUrl(sLongUrl);
                if (aResult.Length > 0)
                {
                    strShort = aResult[iIndex];
                }
            }
            catch
            {

            }
            return strShort;
        }

        /// <summary>
        /// 生成短链接
        /// </summary>
        /// <param name="url"></param>
        /// <returns></returns>
        public static String[] GetshortUrl(String url)
        {
            String[] resUrl = new String[4];
            try
            {
                // 可以自定义生成 MD5 加密字符传前的混合 KEY
                String key = "arcsoft_ascp";
                // 要使用生成 URL 的字符
                String[] chars = new String[] { "a" , "b" , "c" , "d" , "e" , "f" , "g" , "h" ,
              "i" , "j" , "k" , "l" , "m" , "n" , "o" , "p" , "q" , "r" , "s" , "t" ,
              "u" , "v" , "w" , "x" , "y" , "z" , "0" , "1" , "2" , "3" , "4" , "5" ,
              "6" , "7" , "8" , "9" , "A" , "B" , "C" , "D" , "E" , "F" , "G" , "H" ,
              "I" , "J" , "K" , "L" , "M" , "N" , "O" , "P" , "Q" , "R" , "S" , "T" ,
              "U" , "V" , "W" , "X" , "Y" , "Z"
       };
                // 对传入网址进行 MD5 加密
                String sMD5EncryptResult = Common.SecurityHelper.Safe.MD5(key + url, 32);
                String hex = sMD5EncryptResult;


                for (int i = 0; i < 4; i++)
                {
                    // 把加密字符按照 8 位一组 16 进制与 0x3FFFFFFF 进行位与运算
                    String sTempSubString = hex.Substring(i * 8, 8);
                    // 这里需要使用 long 型来转换，因为 Inteper .parseInt() 只能处理 31 位 , 首位为符号位 , 如果不用 long ，则会越界
                    long lHexLong = 0x3FFFFFFF & Convert.ToInt64(sTempSubString, 16);
                    String outChars = "";
                    for (int j = 0; j < 6; j++)
                    {
                        // 把得到的值与 0x0000003D 进行位与运算，取得字符数组 chars 索引
                        long index = 0x0000003D & lHexLong;
                        // 把取得的字符相加
                        outChars += chars[(int)index];
                        // 每次循环按位右移 5 位
                        lHexLong = lHexLong >> 5;
                    }
                    // 把字符串存入对应索引的输出数组
                    resUrl[i] = outChars;
                }
            }
            catch
            {

            }
            return resUrl;
        }

    }
}
